Drivers of Community Composition in Wood-Inhabiting Fungi and Implications for Wood Decay in Temperate Forests Open Access
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Globally, forests account for over half of the carbon stored in terrestrial ecosystems. A substantial portion of this carbon is incorporated into woody plant tissues that have long (year to hundreds of years) residence times in forest ecosystems after plant death. Wood inhabiting fungi play a critical role in the global carbon cycle as the primary decomposers of woody plant biomass in forests. Fungi are some of the only organisms capable of breaking down lignin and cellulose, the primary building blocks of plant woody tissues, the the action of enzymes that specifically target these macromolecules. The composition of fungal communities depends on environmental conditions and the quality of the woody substrate, and in turn affects how quickly wood decay proceeds. These organisms are sensitive to changes in the environment, showing changes in fruiting phenology related to climate change, and in fruiting abundances related to forest management. My dissertation seeks to explore the relationship between fungal community composition and the wood decay process in the context of anthropogenic changes to the environment. First, I used a large-scale forest harvesting experiment to address the question of how different harvesting practices influence the fungal community and wood decay rates. I found that both fungal communities and wood decay rates were structured more strongly by wood species than harvest regime two years post harvest, but that the type of forest harvest might impact the ability of fungi to replace initial wood-decayers as wood decay progresses. Second, I combined repeated surveys of wood fruiting fungi with assays for enzyme activity to determine how fungal fruiting and enzyme activities are influenced by environmental conditions, and whether these two fungal activities are well-coordinated. I found that both activities respond strongly to temperature, but over different timescales. Fruiting and enzyme activities were significantly but weakly correlated, indicating that we cannot extrapolate how fungal ecosystem function might be changing in response to climate change based on changes in fruiting phenology. Finally, I used amplicon sequencing of fungal communities within wood to relate the wood-inhabiting fungal community to enzyme activity to determine how much of the variation in enzyme activity can be attributed to the fungal community and whether certain fungal taxa were particularly related to high enzyme activities. Fungal community composition explain 12 to 26% of the variation in enzyme activity levels, and 14 fungal taxa were related to high enzyme activities. Thus, despite the high diversity of these communities, there are species that might be more important than others for ecosystem function, and these species should be targeted for future studies.